The invention is more particulary applicable to a circuit-breaker insulated with sulphur hexafluoride (SF.sub.6) at a pressure of a few bars.
A gas (e.g. SF.sub.6) insulated circuit-breaker generally interrupts a capacitive current without causing any voltage surge; on the other hand, voltage surges in a ratio exceeding 2:1 may occur when the circuit-breaker interrupts an inductive current such as the load current of a shunt reactance or the current through a high-power transformer with a reactive load.
In the case of very high voltage networks, at voltages above 245 kV, for example, the line circuit-breakers are sometimes fitted with closing resistors which, through closing the circuit in two stages, reduce the amplitude of voltage surges which may occur on the network when closing on an open-circuit line.
The value of this closing resistor is similar to the surge impedance on the line, that is to say 300 to 600 ohms.
To reduce the voltage surges due to the interruption of an inductive current before it passes through zero amplitude it is beneficial to use an opening resistor of higher value, around 2000 ohms.
The use of the closing resistor as the opening resistor has been envisaged; at first sight this solution would appear more economical than providing the circuit-breaker with both a closing resistor and an opening resistor.
However, while a closing resistor may be housed in the opening chamber of a circuit-breaker (on this topic refer to French Patent Application No. 80 16222 dated July 23, 1980 and the first Patent of Addition thereto No. 89 06444 dated Mar. 31, 1981), an opening resistor requires an interrupting device the size of which is inversely proportional to the opening resistor value. It has therefore been preferred to add to a circuit-breaker having a main chamber containing a closing resistor an auxiliary chamber containing an opening resistor.
On this topic reference should be had to 1964 CIGRE (Conference Internationale des Grands Reseaux Electriques) Communication No. 138: "Problemes apparaissant aux tensions les plus elevees lors de la manoeuvre de disjoncteurs" ("Problems arising on operation of circuit-breakers at very high voltages") by E MAURY.
The circuit-breaker described in this communication is equipped with various mechanisms for opening and closing the various main and auxiliary chamber contacts in a predetermined sequence.
This results in a complicated mechanism, but the presence of a source of pressurised gas facilitates the actuation of the various components.
In the case of a circuit-breaker insulated with SF.sub.6 where there is no compressed air supply a simpler mechanism is required, providing for inserting or removing the various opening and closing resistors in a single operation.
One objective of the present invention is to provide a gas-insulated circuit-breaker having at least one closing resistor and at least one opening resistor and mechanisms for inserting and disconnecting said resistors in accordance with sequences required by the operation of the circuit-breaker wherein the insertion mechanisms are simple and require no power source other than that displacing the movable main contacts.